ao_oss: use poll(), drop --disable-audio-select support

Replace select() usage with poll() (and reduce code duplication).

Also, while we're at it, drop --disable-audio-select, since it has the
wrong name anyway. And I have doubts that this is needed anywhere. If
it is, it should probably fallback to doing the right thing by default,
instead of requiring the user to do it manually. Since nobody has done
that yet, and since this configure option has been part of MPlayer ever
since ao_oss was added, it's probably safe to say it's not needed.

The '#ifdef SNDCTL_DSP_GETOSPACE' was pointless, since it's already used
unconditionally in another place.

audio/out/ao_oss.c

@@ -31,6 +31,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#include <poll.h>
 #include <errno.h>
 #include <string.h>
 #include <strings.h>
@@ -219,6 +220,14 @@ static int control(struct ao *ao, enum aocontrol cmd, void *arg)
     return CONTROL_UNKNOWN;
 }
 
+// 1: ok, 0: not writable, -1: error
+static int device_writable(struct ao *ao)
+{
+    struct priv *p = ao->priv;
+    struct pollfd fd = {.fd = p->audio_fd, .events = POLLOUT};
+    return poll(&fd, 1, 0);
+}
+
 // open & setup audio device
 // return: 0=success -1=fail
 static int init(struct ao *ao)
@@ -393,30 +402,22 @@ ac3_retry:
 
     if (p->buffersize == -1) {
         // Measuring buffer size:
-        void *data;
+        void *data = malloc(p->outburst);
+        if (!data) {
+            MP_ERR(ao, "Out of memory, or broken outburst size.\n");
+            return -1;
+        }
         p->buffersize = 0;
-#if HAVE_AUDIO_SELECT
-        data = malloc(p->outburst);
         memset(data, 0, p->outburst);
-        while (p->buffersize < 0x40000) {
-            fd_set rfds;
-            struct timeval tv;
-            FD_ZERO(&rfds);
-            FD_SET(p->audio_fd, &rfds);
-            tv.tv_sec = 0;
-            tv.tv_usec = 0;
-            if (!select(p->audio_fd + 1, NULL, &rfds, NULL, &tv))
-                break;
+        while (p->buffersize < 0x40000 && device_writable(ao) > 0) {
             write(p->audio_fd, data, p->outburst);
             p->buffersize += p->outburst;
         }
         free(data);
         if (p->buffersize == 0) {
-            MP_ERR(ao, "***  Your audio driver DOES NOT support select()  ***\n");
-            MP_ERR(ao, "Recompile mpv with #define HAVE_AUDIO_SELECT 0 in config.h!\n");
+            MP_ERR(ao, "Your OSS audio driver DOES NOT support poll().\n");
             return -1;
         }
-#endif
     }
 
     ao->bps = ao->channels.num * af_fmt2bps(ao->format);
@@ -500,28 +501,12 @@ static int get_space(struct ao *ao)
 {
     struct priv *p = ao->priv;
 
-#ifdef SNDCTL_DSP_GETOSPACE
     if (ioctl(p->audio_fd, SNDCTL_DSP_GETOSPACE, &p->zz) != -1) {
         // calculate exact buffer space:
         return p->zz.fragments * p->zz.fragsize / ao->sstride;
     }
-#endif
 
-    // check buffer
-#if HAVE_AUDIO_SELECT
-    {
-        fd_set rfds;
-        struct timeval tv;
-        FD_ZERO(&rfds);
-        FD_SET(p->audio_fd, &rfds);
-        tv.tv_sec = 0;
-        tv.tv_usec = 0;
-        if (!select(p->audio_fd + 1, NULL, &rfds, NULL, &tv))
-            return 0;                                            // not block!
-    }
-#endif
-
-    return p->outburst / ao->sstride;
+    return device_writable(ao) > 0 ? p->outburst / ao->sstride : 0;
 }
 
 // stop playing, keep buffers (for pause)

old-configure

@@ -213,7 +213,6 @@ options_state_machine() {
     opt_yes_no _portaudio   "PortAudio audio output"
     opt_yes_no _jack        "JACK audio output"
     opt_yes_no _openal      "OpenAL audio output"
-    opt_yes_no _select      "using select() on the audio device" yes
     opt_yes_no _shm         "X11/Xv shared memory"
     opt_yes_no _lua         "Lua scripting"
     opt_yes_no _encoding    "encoding functionality" yes
@@ -542,8 +541,6 @@ define_yes_no $_termios_ok HAVE_TERMIOS
 check_statement_libs "shm" $_shm SHM "sys/types.h sys/ipc.h sys/shm.h" \
     "shmget(0, 0, 0); shmat(0, 0, 0); shmctl(0, 0, 0);"
 
-check_trivial "audio select()" $_select AUDIO_SELECT
-
 echocheck "pkg-config"
 if $($_pkg_config --version > /dev/null 2>&1); then
   if test "$_ld_static"; then

wscript

@@ -458,11 +458,6 @@ audio_output_features = [
         'func': check_true,
         'deps_any': [ 'oss-audio-native', 'oss-audio-sunaudio',
                       'oss-audio-4front' ]
-    }, {
-        'name': '--audio-select',
-        'desc': 'audio select()',
-        'deps': [ 'oss-audio' ],
-        'func': check_true,
     }, {
         'name': '--rsound',
         'desc': 'RSound audio output',